In general, a fuel cell comprises a cell on which an air electrode layer, an electrolyte layer and a fuel electrode layer are laminated, a fuel-supplying part for supplying fuel as a reducing agent to the fuel electrode layer and an air-supplying part for supplying air as an oxidizing agent to the air electrode layer, and it is an electric cell in which electrochemical reaction takes place in the cell of a fuel cell between fuel and oxygen in the air to provide electric power to the outside. Fuel cells of various types are developed.
In recent years, because of a rise in consciousness to environmental problems and energy saving, it is studied to use a fuel cell as a clean energy source for various applications. In particular, attentions have been paid to fuel cells which can generate electric power by only supplying directly a liquid fuel comprising methanol and water (refer to, for example, patent documents 1 and 2).
Among them, liquid fuel type fuel cells making use of capillary force for supplying a liquid fuel are known (refer to, for example, patent documents 3 to 7).
Liquid fuel type fuel cells described in the above respective patent documents supply a liquid fuel from a fuel tank to a fuel electrode by virtue of capillary force, and therefore they do not require a pump for sending a liquid fuel with pressure, so that they have merits in reducing a size.
Such liquid fuel type fuel cells as merely making use of capillary force of a porous body and/or a fiber bundle disposed in a fuel-storing tank are suited to reduction in a size in terms of constitution, but because fuel is supplied directly to a fuel electrode in the form of liquid, the fuel follows imperfectly during use over a long period of time under a use situation in which it is mounted in a small-sized portable appliances and in which the attitude of a cell part is changed very often in every direction, and the trouble that the fuel is cut off from being supplied is brought about, so that it causes inhibiting the fuel from being supplied constantly to an electrolyte layer.
On the other hand, known as one of countermeasures for solving the above defects is a fuel cell system in which a liquid fuel is introduced into a cell by virtue of capillary force and in which the liquid fuel is then vaporized in a fuel-vaporizing layer and used (refer to, for example, a patent document 8). However, it has the problem that poor followability of the fuel, which is a fundamental problem, is not improved, and involved therein is the problem that it is difficult to reduce a size of the fuel cell having the above structure because of a system in which a liquid is vaporized and then used as fuel.
As described above, in conventional fuel cells, the existing situation is that a liquid fuel is instably supplied in supplying the fuel directly to a fuel electrode to cause fluctuation in an output value during operation and that it is difficult to reduce a size thereof to such an extent that they can be mounted in portable appliances while maintaining stable characteristics.
When a conventional resin, for example, polyethylene is used as a material for a fuel tank, it is considered that a liquid fuel itself permeates the resin in storage over a long period of time or vaporization and leaking of the liquid fuel from joints of parts of a fuel tank take place, so that loss of the fuel is likely to be brought about. In this case, if the respective resinous members are constituted in such thicknesses that vaporization and leaking are not caused in order to prevent vaporization and leaking of the fuel, brought about is the problem that not only the purpose of reducing a size of the fuel cell main body can not be achieved but also it becomes difficult to observe a remaining amount of the liquid fuel. Further, when materials such as metal and glass are used for a material constituting a fuel tank, involved therein are the problems that if the material is made of metal, it is impossible to know a remaining amount of a liquid fuel and an amount of the fuel remaining in a fuel tank can not be observed and that if the material is made of glass, management in processing and assembling is troublesome to result in a rise in the cost and deformation and breakage are liable to take place.
Further, if a fuel cell having a fuel-storing tank and electronic appliances in which a fuel cell is mounted are left standing in a place where temperature is elevated in a certain case such as the vicinity of a front glass when fuel having a low boiling point such as methanol is used as a liquid fuel, the fuel having a low boiling point boils, so that all of it is vaporized and lost in a certain case. A method in which a substance for causing a rise in a boiling point is mixed with the liquid fuel is considered as a countermeasure for solving the above problems, but involved therein is the problem that if foreign matters are mixed in the liquid fuel, an adverse effect is exerted on electrode reaction in a certain case.
Also, a method in which the whole part of a fuel-storing tank is pressurized is considered as a method for raising an apparent boiling point of a liquid fuel. In this case, metals, glass and conventional resins are considered as a material constituting the fuel-storing tank which can endure the pressurization. As described above, however, involved therein are the respective problems that if the material is made of metal, it is impossible to observe a remaining amount of a liquid fuel; if the material is made of glass, management in processing and assembling is troublesome to result in a rise in the cost; and if the material is made of a resin, the liquid fuel and gas for pressurization are liable to vaporize or leak. Further, there is the problem that deformation and the like are liable to take place.
Further, known as a fuel cell in which pressurized gas is used as a supplying device for a liquid fuel is, for example, a fuel cell equipped with a vessel containing therein a liquid fuel and pressurized gas for pressurizing the liquid fuel to send to the fuel cell with pressure and a means for attach/detaching the vessel to and from a fuel-supplying passage for the fuel cell (refer to, for example, patent document 9).
However, in the above fuel cell in which a liquid fuel is supplied with pressurized gas, increase in a size of the device is brought about because the liquid fuel is controlled by means of a flow rate-controlling valve provided in a fuel-supplying passage, and a problem is still involved in mounting it on devices of a portable type. Further, the existing situation is that if the vessel is tilted from right to left or up and down, the liquid fuel can not be supplied well to exert an adverse effect on power generation efficiency.
Patent document 1: Japanese Patent Application Laid-Open No. 258760/1993 (claims, examples and others)
Patent document 2: Japanese Patent Application Laid-Open No. 307970/1993 (claims, examples and others)
Patent document 3: Japanese Patent Application Laid-Open No. 66066/1984 (claims, examples and others)
Patent document 4: Japanese Patent Application Laid-Open No. 188008/1994 (claims, examples and others)
Patent document 5: Japanese Patent Application Laid-Open No. 229158/2003 (claims, examples and others)
Patent document 6: Japanese Patent Application Laid-Open No. 299946/2003 (claims, examples and others)
Patent document 7: Japanese Patent Application Laid-Open No. 340273/2003 (claims, examples and others)
Patent document 8: Japanese Patent Application Laid-Open No. 102069/2001 (claims, examples and others)
Patent document 9: Japanese Patent Application Laid-Open No. 317755/2003 (claims, examples and others)